The present invention relates to novel apparatus and method for operating a tufting machine so as to avoid the production of stop marks in the pile fabric during such time that the tufting machine is not normally operating.
As is well-known in the carpet industry, a defect which often occurs during the production of tufted carpet when tufting machines are stopped or restarted is known as a stop mark or tufting streak. These stop marks are defects which are readily visible and appear on the face of the pile of the tufted carpet and generally extend across the full width thereof. This stop mark typically results when the row or rows of tuft loops closest to the needles, i.e., the last formed row of tufts, has the yarn pulled therefrom so that the height of the yarn forming the piles is less than it should be.
Various approaches are disclosed in the prior art in attempting to overcome this problem of stop marks. Beasley U.S. Pat. Nos. 2,840,019 and 2,857,867 address the problem of elimination of stop marks by providing an overfeed mechanism for the backing fabric that is fed to the tufting needles. Essentially, a locking type of drive train is disclosed so as to prevent any reverse movement of the backing fabric through the machine upon a start-up after the tufting machine had once been stopped.
Jackson U.S. Pat. No. 3,529,560 addresses the problem of stop marks by having the loopers clear the pile loops during such stoppage. This patent discloses stopping of the needle bar in an up position with the machine loopers clear of the the immediately formed pile loops so as to relieve yarn tension and eliminate stop marks.
Colbert U.S. Pat. No. 3,548,766 discloses an auxiliary drive that comes into operation upon stoppage of the tufting machine for the purpose of causing a pair of puller rolls to continuously rotate and slippingly engage the tufting yarns without feeding the yarns so as to maintain the yarns under tension rearwardly thereof and prevent the retraction of the yarns forwardly beyond the puller rolls. Stated somewhat differently, the puller rolls of Colbert serve for preventing an increase or buildup in the tension in the tufting yarns from causing a robbing action of the last formed row of tufts.
Cobble U.S. Pat. No. 3,762,346 discloses a device for relaxing the tufting yarns when the tufting machine is stopped so as to reduce the tension in the yarns that would otherwise cause the yarns to reduce the height of the last formed row of tufts.
Long et al U.S. Pat. No. 4,151,805 discloses a soft start-up mechanism for a tufting machine so as to avoid creation of stop marks as by the jerking of the pile yarns during start-ups wherein no soft start-up is employed. This patent also discloses an actuation of the yarn feed system ahead of restarting the main drive motor for the tufting machine.
With the foregoing prior art approaches in mind, it will be understood that the problem of stop marks is a long existing problem and one to which no universal solution has apparently been found. Applicant's analysis of the problem has led to a very simple solution which it is believed may be more universally applied to most any type of tufting machine for elimination of the problem of stop marks in the tufted fabric.
Briefly stated, this invention recognizes that the high tension present in the tufting yarns being fed to the tufting needles is essentially the cause of robbing of pile loops and creation of stop marks in fabric. It has been determined that upon stoppage of the tufting machine, if in response to such stoppage a small amount of tufting yarn, i.e., a relatively small incremental length of tufting yarn, is immediately fed forwardly from the feed rolls, that the tension in the yarn between the feed rolls and the last formed row of pile tufts will be so relieved as to avoid any robbing action of the last row of pile tufts. It has further been found that if the tufting machine is stopped for a prolonged period of time, that additional incremental amounts of tufting yarn may be fed to avoid build up of tension in the yarn from the feed rolls to the last row of pile tufts. Thus, in the simplest form, this invention solves the problem of formation of stop marks by the positive feed of an incremental length of the tufting yarns forwardly upon stoppage of the tufting machine. This is accomplished by an auxiliary drive means connected to the yarn feed rolls for feeding the tufting yarns forwardly a predetermined amount in response to stoppage of the main drive shaft.